Monday, the Human Rights Campaign said 21 major U.S. corporations have earned the group's top rating for how they treat homosexual, bisexual and transgender employees and consumers.

Last year, 11 earned top marks.

"What we see this year is improvement in every category measured, from written nondiscrimination policies to domestic partner benefits insurance and beyond," said Kim Mills, HRC's education director. "The bottom line is that successful businesses are increasingly recognizing that equality works."

Cracker Barrel Old Country Stores, Emerson Electric Co. and Lockheed Martin Corp. were cited for making major improvements in their workplace equality ratings for such things as adding sexual orientation to nondiscrimination policies, offering diversity training that covers workplace diversity issues or implementing domestic partner benefits.

HRC said the five lowest-scoring companies were Aramark Corp., Domino's Inc., ExxonMobil Corp., Meijer Inc. and National Gypsum Co.

Domino's spokesman Tim McIntyre told CNN that his company has added sexual orientation to its anti-harassment policy and said that Domino's "wants to be an employer of choice for anyone who wants to work hard."

He said that though domestic partner benefits were "on the table for discussion," employees preferred options for existing long-term care for family members such as aging parents.

"For us, it's a cost issue rather than an anti-anything issue," McIntyre said.

ExxonMobil spokeswoman Sandy Duhe said her company's harassment and antidiscrimination policy is an "all-inclusive global policy -- no reasons, no excuses, nothing tolerated by any employee or contractor anywhere in the world."

She said ExxonMobil's policy on domestic-partner benefits depends on the national regulations of whatever country in which the employees reside. Gay couples in the Netherlands and Canada, for example, are offered domestic-partner benefits, but those in the United States are not.